A generic device for the concentration of solar radiation in an absorber has become known from WO 2012/145774. The device has an inflatable concentrator which is formed by an elongated, substantially cylindrical tubular sleeve of a plurality of film elements. On the top side, the cushion has a transparent entry window for the solar radiation to pass through. Provision is further made for a reflector film by means of which the cushion is sub-divided into at least two separate pressure chambers. The reflector film has a reflecting surface by means of which the coupled-in solar radiation is focused in the direction of an absorber. For anchoring the concentrator, provision is made for an anchoring frame. The anchoring frame has a tracking system, so that the cushion-shaped concentrator can track the sun's path. The tracking system has a plurality of tracking rings which surround the concentrator cushion and which are rotatably supported by means of rolling devices. The tracking rings are supported on bottom-side base elements. To effect the pivoting of the concentrator, the tracking rings are secured to the longitudinal sides of the concentrator cushion via local, substantially square, retaining plates.
Due to the pressure difference between the two pressure chambers of the concentrator the reflecting surface is curved concavely, so that the incident solar radiation is focused in the absorber. In practice it has turned out that the efficiency of the concentrator is impaired by the fact that the curvature of the reflecting film deviates from the parabolic shape which would enable optimum focusing of the solar radiation.
To mitigate this problem US 2009/0260620 A1 suggested an inflatable solar collector in which the lower hollow space is provided with correction chambers laterally beneath the reflecting film. The pressure relations in the correction chambers were chosen such that the reflecting film is adapted more strongly to the parabolic shape.
This measure, however, has turned out to be insufficient since the pressure differences in the correction chambers have an effect on the geometry of the flexible side walls of the solar collector, which are in turn connected to the reflector film. Thus, the curvature of the reflector film may be modified in an unpredictable manner. Moreover, the pressures in the correction chambers disadvantageously would have to be adjusted very accurately to adapt the curvature of the reflector film by exerting pressure from the underside. Accordingly, the prior art requires a complex control and/or regulation of the pressure relations. Due to the influence of the correction chambers on the flexible film structure of the solar collector the reflector film can be adapted only inaccurately to the parabolic shape even if the pressure relations are adjusted accurately. Moreover, it is a disadvantage in the prior art that at least two correction chambers have to be provided at the longitudinal sides. This aggravates the manufacturing, assembling, and operating of the solar collector.
According to this, it is the object of the invention at hand to eliminate or to ease, respectively, the disadvantages of the prior art. The invention thus in particular has the goal of creating a device of the above-specified type by means of which it is possible to accurately adjust the curvature of the reflector film with constructionally simple means to increase the efficiency of energy conversion.
This object is solved by means of a device for concentration of solar radiation in an absorber, comprising an inflatable concentrator cushion which comprises a cover film element comprising a light-permeable entry window for coupling in solar radiation and a reflector film for the concentration of the solar radiation in an absorber, the reflector film sub-dividing the concentrator cushion into at least two hollow spaces and having a curvature in an inflated state of the concentrator cushion, a pivoting apparatus by means of which the concentrator cushion is pivotable, a retaining apparatus mounted to the pivoting apparatus, for retaining the concentrator cushion, and an adjusting device for adjusting the curvature of the reflector film of the concentrator cushion, wherein the retaining apparatus comprises a lower longitudinal member which extends in a longitudinal direction of the concentrator cushion and which is connected to a bottom film element of the concentrator cushion, wherein the adjusting device for adjusting the curvature of the reflector film comprises a tensioning element between the lower longitudinal member of the retaining apparatus and the reflector film, said tensioning element being connected on one side to the reflector film and on another side to the lower longitudinal member of the retaining apparatus. Embodiments are specified in the dependent claims.
According to the invention, the retaining apparatus comprises a lower longitudinal member which extends in the longitudinal direction of the concentrator cushion and which is connected with a bottom film element of the concentrator cushion, wherein the adjusting device for adjusting the curvature of the reflector film comprises a tensioning element between the lower longitudinal member of the retaining apparatus and the reflector film, wherein the tensioning element is connected on the one side with the reflector film and on the other side with the lower longitudinal member of the retaining apparatus.
Accordingly, the elongated concentrator cushion which has preferably a substantially cylindrical cross-section is secured at the lower side to the lower longitudinal member of the retaining apparatus. For the purpose of the instant disclosure the terms “top or upper” and “bottom or lower” always refer to the operating position of the device, wherein the bottom film element of the concentrator cushion faces an underground and/or a soil structure at the site of use. In the operating state the lower side of the concentrator cushion is fixed in the region of the bottom film element to the lower longitudinal member which is manufactured of a substantially rigid material, i.e. a material substantially non-resilient to operating forces, especially metal. This makes it possible to achieve a stable support of the concentrator cushion. The pressure difference between the upper hollow space and the lower hollow space of the concentrator cushion causes in the inflated operating state a substantially two-dimensional curvature of the reflector film which remains constant in the longitudinal direction of the concentrator cushion and by means of which a focusing of the incident solar radiation in the absorber inside the upper hollow space is accomplished. For achieving a high efficiency of the concentrator cushion it is essential that the solar radiation is focused accurately in the region of the absorber. The deflection of the reflector film due to the pressure difference between the upper and the lower hollow spaces of the concentrator cushion would, without further measures, deviate from the parabolic shape which would promise the maximum energy yield. For approaching the curvature of the reflector film to the parabolic shape, provision is made in accordance with the invention for a tensioning element which is connected on the one side with the reflector film and on the other side with the lower longitudinal member of the retaining apparatus. In the tensioned state of the tensioning element in operation of the concentrator an additional tensile force is transferred to the reflector film by means of the tensioning element, which causes a slight stretching of reflecting sections of the reflector film. This makes it possible to reduce the deviation of the reflecting surface from the ideal parabolic shape. Advantageously, the energy yield of the concentrator cushion may be increased distinctly by this simple measure. The arrangement of the tensioning element in accordance with the invention enables a much more accurate adaptation of the cross-sectional geometry of the reflector film than the prior art of US 2009/0260620 A1 in which additional pressure chambers were arranged directly beneath the reflector film. Contrary to this, the tensioning element according to the invention causes a kink or constriction of the reflector film in the region of the connection between the tensioning element and the reflector film. The tensioning element thus achieves a deviation from the continuous cross-section course of the reflector film which results from the pressure difference between the upper hollow space and the lower hollow space of the concentrator cushion. On both sides of the contact area of the tensioning element at the reflector film two reflecting sections are formed by means of which the incident solar radiation is reflected in the absorber. Advantageously, the tensile force transferred by the tensioning element to the reflector film can be adjusted substantially more accurately and easily than the slight pressure differences in the correction chambers of prior art by means of which likewise a certain adaptation of the curvature of the reflector film should have been effected. In accordance with the invention the adjustment of the reflector film is additionally facilitated in that the tensioning element is secured to the lower longitudinal member of the retaining apparatus, which is, in the inflated state of the concentrator cushion, arranged to be substantially rigid or immobile. Contrary to this, the correction chambers in prior art may cause certain deformations on the resilient side walls of the known solar collector, which have in turn a disadvantageous effect on the shape of the reflector film. In accordance with the invention these disadvantages are avoided in that the tensioning element is secured to the substantially rigid lower longitudinal member of the retaining apparatus. Thus, the tensile force of the tensioning element may be converted substantially completely to a deformation of the reflector film. Due to the resilience and/or inherent elasticity of the reflector film the reflector film is, in the region of the contact area of the tensioning element, pulled slightly downward, in the direction of the lower longitudinal member, so that the curvature or indentation of the reflecting surface in cross-section is approached to the desired parabolic shape.
To divide the reflecting surface of the reflector film into two reflecting sections of substantially identical design it is beneficial if the tensioning element is connected with a middle longitudinal section of the reflector film, which extends substantially centrally between the longitudinal edges of the reflector film in the longitudinal direction of the concentrator cushion. In this embodiment the tensioning element is adapted to transfer a tensile force to the middle longitudinal section of the reflector film, which extends, in the inflated state of the concentrator cushion, substantially in the middle between the longitudinal edges of the reflector film which extend in parallel to the longitudinal direction of the concentrator cushion. The tensioning element divides the reflecting surface into two reflecting sections extending in the longitudinal direction of the concentrator cushion, which extend, starting out from the contact area of the tensioning element at the middle longitudinal section of the reflector film, to the two longitudinal edges of the reflector film. Due to the curvature of the reflector film in the inflated state of the concentrator cushion the middle longitudinal section of the reflector film has the shortest distance to the lower longitudinal member of the retaining apparatus to which the tensioning element is secured. Due to the tensile force on the middle longitudinal section of the reflector film the two reflecting sections are slightly stretched, wherein the two reflecting sections are separated from each other by a discontinuity, i.e. a kink or an indentation, of the reflector film. Thus, it is possible to adapt the cross-section of the reflector film more strongly to a parabolic shape. Advantageously, the energy yield of the concentrator may thus be further increased.
To focus the solar radiation accurately on the absorber extending in the longitudinal direction of the concentrator cushion it is beneficial if the tensioning element is, over substantially the entire length of the reflector film, connected with the reflector film and the lower longitudinal member. Accordingly the contact area of the tensioning element at the reflector film in the longitudinal direction of the concentrator cushion extends substantially over the entire length of the reflector film. Thus, the cross-sectional geometry of the reflector film in the longitudinal direction of the concentrator cushion may be kept substantially constant to achieve a constant focusing of the solar radiation along the absorber.
For designing the concentrator cushion as a film compound it is beneficial if the tensioning element comprises a tensioning film element which, in the inflated state of the concentrator cushion, is tensioned between the lower longitudinal member and the reflector film. In this embodiment the concentrator cushion is formed by a film structure comprising at least the cover film element, the bottom film element, possibly additionally two side wall film elements, and the tensioning film element. In the uninflated state the film structure of the concentrator cushion is adapted to be arranged in a flat, layered position. Thus it is possible to store the concentrator cushion in a space-saving manner. Moreover, transportation to the site of use is facilitated. It is in particular of advantage that the film structure of the concentrator cushion, including the tensioning film element for adjusting the curvature of the reflector film, may be rolled upon a roll in the uninflated state for preparation of transportation. The film elements of the concentrator cushion, i.e. especially the cover film element, the bottom film element, or the tensioning film element, are preferably manufactured of resilient, thin-walled plastic materials.
For transferring a tensile force to the middle longitudinal section of the reflector film it is of advantage if the tensioning film element comprises a tensioning section contacting the middle longitudinal section of the reflector film substantially rectangularly. Accordingly, the tensioning section of the tensioning film element is, in the inflated operating state of the concentrator cushion, arranged substantially perpendicular to the reflector film in the region of the contact area of the tensioning element, wherein the tensioning section of the tensioning film element is flat or plane, respectively. In this embodiment the cross-sectional area of the tensioning film element in the region of the tensioning section corresponds substantially to the wall strength of the film piece with which the tensioning section is formed. This embodiment advantageously has the effect that the tensile force is transferred merely locally at the contact area of the tensioning section. This may ensure that the reflector film is tensioned evenly on both sides of the contact area of the tensioning element at the reflector film. The tensioning section of the tensioning film element is connected with the reflector film in a suitable manner. The tensioning section may, for instance, transit into a securing section of the tensioning film element which is connected with the reflector film by means of a join connection, for instance, a seam.
In accordance with a particularly preferred embodiment the tensioning film element comprises an inflatable hollow chamber for adjusting the distance between the lower longitudinal member and the reflector film by inflating the hollow chamber of the tensioning film element. In this embodiment it is possible to accurately adjust and readjust the curvature of the reflector film in a particularly simple manner. For this purpose, the tensioning film element comprises an inflatable hollow chamber, i.e. a hollow chamber adapted to be filled with air. Due to the resilience of the tensioning film element it is possible to adapt the shape of the tensioning film element by filling the hollow chamber. By inflating the hollow chamber, i.e. by filling it with air, the tensioning film element may be transferred from a stretched state to a shortened state so as to shorten the height of the tensioning film element, i.e. the distance between the lower contact area of the tensioning film element at the lower longitudinal member of the retaining apparatus and the upper contact area of the tensioning film element at the reflector film. Depending on the filling pressure of the hollow chamber of the tensioning film element the tensile force on the reflector film may be increased or decreased for adjusting or readjusting the bending of the reflector film. Accordingly, in the inflated state of the hollow chamber of the tensioning film element a higher tensile force may be exerted on the reflector film than in the uninflated state of the hollow chamber. This embodiment comprises a number of advantages. Firstly, the curvature of the reflector film may be varied smooth as well as continuously via the filling pressure of the hollow chamber. Secondly, an adaptation of the tension of the reflector film may be performed during the running operation of the concentrator. For this purpose it is beneficial if the hollow chamber of the tensioning film element is connected with an air supply device by which the filling pressure of the hollow chamber and hence the cross-sectional geometry of the tensioning film element is adjustable in the inflated operating state of the concentrator cushion. Preferably, the air supply device is connected with an air pressure sensor by which the filling pressure of the hollow chamber of the tensioning film element can be measured. Advantageously, variations in the geometry of the reflector film may be taken into account in this embodiment during the running operation of the device. In practice, various factors influencing the curvature of the reflector film have to be taken into account. These include especially the ambient temperature at the site of use of the concentrator, the long-term behavior of the plastic materials of the concentrator cushion, or pressure losses in the hollow spaces of the concentrator cushion and/or in the hollow chamber of the tensioning film element. The embodiment of the tensioning film element with the hollow chamber entails, thirdly, the advantage that the device for adjusting the curvature of the reflector film is integrated in the film structure of the concentrator cushion. This makes it possible to renounce rigid adjusting means which would aggravate or prevent the folding or rolling of the concentrator cushion in the uninflated state. Moreover it is, fourthly, beneficial that the volume changes of the hollow chamber of the tensioning film element are, as compared to the distance changes between the reflector film and the lower longitudinal member, comparatively large. This makes it possible to adjust the reflector film accurately even if the air pressure inside the hollow chamber of the tensioning film element can be adjusted with limited accuracy only and this is, moreover, subject to certain fluctuations.
For dissipating the loads acting on the concentrator cushion in operation, such as wind loads, it is beneficial if the lower longitudinal member is connected in a substantially air-tight manner with the longitudinal edges of the bottom film element of the concentrator cushion, which confine a lower passage opening of the concentrator cushion. In this embodiment the bottom film element therefore comprises a lower passage opening for passage of the lower longitudinal member of the retaining apparatus. The longitudinal edges of the bottom film element adjacent to the lower passage opening are connected in a substantially air-tight manner with the longitudinal sides of the lower longitudinal support, so that undesired escape of air from the lower hollow space of the concentrator cushion is prevented substantially completely.
In accordance with a particularly preferred embodiment the lower longitudinal member comprises longitudinal belts, which are connected to one another via filling bars, for a substantially air-tight connection with the longitudinal edges of the bottom film element which confine the lower passage opening, wherein provision is made between the longitudinal belts for a sealing film strip which bridges the lower passage opening of the concentrator cushion. Accordingly, the retaining apparatus passes through a lower passage opening at the lower side of the concentrator cushion, said lower passage opening being sealed on all sides. The lower longitudinal member comprises in this embodiment at least two elongated longitudinal belts which, based on the circumferential direction of the concentrator cushion, are arranged at a distance to one another. Provision is made between the longitudinal belts for a sealing film strip which bridges the lower passage opening of the concentrator cushion. For forming the longitudinal belts, rod elements are preferably provided, which have in particular a substantially circular cross-section. By the arrangement of the sealing film strip the passage opening between the longitudinal belts of the longitudinal member is closed substantially in an air-tight manner, so that the connection between the longitudinal belts of the longitudinal member itself need not be designed to be air-tight.
For increasing the stability of the lower longitudinal member it is of advantage if the lower longitudinal member comprises at least two further longitudinal belts which extend in parallel to the longitudinal belts in the longitudinal direction of the concentrator cushion. Preferably, the longitudinal members have a substantially rectangular, especially substantially square, cross-section, wherein the upper corners are formed by the longitudinal belts and the lower corners by the further longitudinal belts. For achieving a maximum volume of the concentrator cushion inside the pivoting apparatus it is of advantage if the further longitudinal belts of the lower longitudinal member are arranged inside the lower hollow space of the concentrator cushion. In this embodiment the longitudinal belts of the lower longitudinal member extend substantially in the plane of the bottom film element, wherein the further longitudinal belts of the lower longitudinal member are arranged in the lower hollow space of the concentrator cushion. Advantageously, the mounting volume available inside the pivoting apparatus may thus be utilized optimally.
Preferably, the longitudinal belts and/or the further longitudinal belts of the upper longitudinal member are connected to one another via filling bars, wherein preferably further filling bars are provided between the longitudinal belts and the further longitudinal belts. Thus, the longitudinal members are designed as trussed beams.
To connect the concentrator cushion to the lower longitudinal member, it is preferably provided that, at the longitudinal belts of the lower longitudinal member, a profile element in each case is arranged, which is connected to a connecting element for the substantially air-tight connection to one of the longitudinal edges of the bottom film element and to a further connecting element for the substantially air-tight connection to one of the longitudinal edges of the sealing film strip.
To make the connections between the lower longitudinal member and the concentrator cushion substantially air-tight, various sealants may be provided.
To seal the connection between the lower longitudinal member and the concentrator cushion it is beneficial if a keder rail is provided as connecting element, in which a keder element is arranged at the longitudinal edges of the bottom film element. In this embodiment a keder device is therefore provided as a sealant between the concentrator cushion and the lower longitudinal member, said keder device being formed by the keder elements and the corresponding keder rails. The keder elements extend over the length of the longitudinal edges of the bottom film element. At the longitudinal belts of the lower longitudinal member appropriate keder rails are provided which extend in the longitudinal direction of the lower longitudinal member and thus in parallel to the longitudinal edges of the bottom film element. The keder element has a larger cross-section than the bottom film element, wherein the keder element is preferably designed with a round, especially circular, cross-section. Due to the pressure in the lower hollow space of the concentrator cushion the bottom film element is available in a tensioned state, so that the keder elements are pressed against the inner walls of the keder rails at the longitudinal edges of the bottom film element. Thus, a substantially air-tight connection of the concentrator cushion with the lower longitudinal member is achieved, which has turned out to be particularly reliable.
To connect the sealing film strip correspondingly in a substantially air-tight manner with the longitudinal belts of the lower longitudinal member it is favorable if, as a further connecting element, a further keder rail is provided in which a further keder element is arranged at one of the longitudinal edges of the sealing film strip. In this embodiment keder rails are provided at the opposing longitudinal edges of each profile element, which keder rails are preferably of substantially identical design. Accordingly each profile element is connected outwardly to one of the longitudinal edges of the bottom film element and inwardly to one of the longitudinal edges of the sealing film strip.
According to an alternative embodiment of the sealants between the concentrator cushion and the lower longitudinal member, a clamping part is provided as connecting element for clamping one of the longitudinal edges of the bottom film element and/or a further clamping part as further connecting element for clamping one of the longitudinal edges of the sealing film strip. In the case of this embodiment, the longitudinal edges of the bottom film element adjacent to the lower passage opening for the upper longitudinal member are clamped between seats of the clamping part or of the profile element, respectively. By means of the clamping, the bottom film element is connected to the lower longitudinal member in a substantially air-tight manner. The sealing film strip between the longitudinal belts of the lower longitudinal member can correspondingly be clamped to the longitudinal belts of the lower longitudinal member in a substantially air-tight manner by means of further clamping parts.
In accordance with a further embodiment a provision is made for a zipper element as connecting element for the connection to a corresponding zipper element on one of the longitudinal edges of the bottom film element and/or for a further zipper element as further connecting element for the connection to a corresponding further zipper element of the sealing film strip.
For forming the hollow chamber of the tensioning film element provision is made in accordance with a preferred embodiment that the profile elements at the longitudinal belts of the lower longitudinal member are each connected to a securing element for the substantially air-tight connection with a film strip confining the hollow chamber of the tensioning film element. In this embodiment, at the longitudinal belts of the lower longitudinal member not only the connecting elements for the bottom film element and the sealing film strip are provided, but additionally the securing elements for two film strips of the tensioning film element which confine the hollow chamber of the tensioning film element by which the curvature of the reflector film is adjusted. Accordingly, the hollow chamber of the tensioning film element is, in this embodiment, confined by the two film strips of the tensioning film element and the sealing film strip between the longitudinal belts of the lower longitudinal member. To prevent air from escaping from the hollow chamber of the tensioning film element into the lower hollow space of the concentrator cushion substantially completely, the film strips of the tensioning film element inside the lower hollow space of the concentrator cushion are connected in a substantially air-tight manner to the securing elements at the longitudinal belts of the lower longitudinal member. The securing elements for the film strips of the tensioning film element may be of substantially identical design as the connecting elements for the bottom film element or the sealing film strip, respectively. As securing elements preferably keder rails extending in the longitudinal direction of the lower longitudinal member are provided, in which corresponding keder elements are arranged at the lower longitudinal edges of the film strips of the tensioning film element.
In accordance with an alternative preferred embodiment the lower longitudinal member comprises, substantially in the middle between the longitudinal belts, an upper-side securing element for securing the tensioning film element. In this embodiment the securing element for the tensioning film element extends in the longitudinal direction of the concentrator cushion substantially at equal distances to the longitudinal belts of the lower longitudinal member. For the upper-side securing to the lower longitudinal member the tensioning film element comprises preferably a securing section which is flat or plane in the inflated state of the concentrator cushion. This shall mean that the cross-sectional area of the tensioning film element in the region of the securing section corresponds substantially to the wall thickness of the securing section. In this embodiment it is favorable if the tensioning film element is connected with the securing element in a substantially air-tight manner by means of the securing section. For this purpose the upper-side securing element for the tensioning film element may be of substantially identical design as the connecting elements for the bottom film element and/or the sealing film strip. Accordingly, especially a keder rail extending in the longitudinal direction of the lower longitudinal member, in which a corresponding keder element is arranged at the lower longitudinal edge of the tensioning film element, may be provided as upper-side securing element.
In accordance with a particularly preferred embodiment the retaining apparatus comprises an upper longitudinal member extending in the longitudinal direction of the concentrator cushion, wherein the upper longitudinal member is connected in a substantially air-tight manner to the longitudinal edges of the cover film element of the concentrator cushion which confine an upper passage opening of the concentrator cushion. In this embodiment the elongated concentrator cushion which preferably has a substantially cylindrical cross-section is secured at the top side to the upper longitudinal member and at the bottom side to the lower longitudinal member. The upper longitudinal member is adapted for suspension of the absorber which is, in the inflated operating state, arranged inside the upper hollow space of the concentrator cushion. The lower longitudinal member is, as described before, adapted for supporting the concentrator cushion at the lower side, on the one hand, and for securing the tensioning element by which the curvature of the reflector foil may be adjusted, on the other hand. Preferably, the concentrator cushion is arranged exclusively at the upper and the lower longitudinal members. Extensive tests revealed that it is particularly advantageous if the two bearing positions for the concentrator cushion, i.e. the upper and the lower longitudinal members, are arranged away from the reflector film or reflective film, respectively, as far away as possible from a geometric aspect. According to the invention, the concentrator cushion is thus fixed on its top side and on its bottom side. In contrast, it is advantageous if the longitudinal sides of the concentrator cushion, in particular in the area of the longitudinal edges of the reflector film, are arranged so as to be capable of being expanded in the radial direction. A thermal expansion of the concentrator cushion can thus be released in particular in the area of the reflector film, whereby the concave geometry of the reflector film is accurately adhered to for the focusing of the solar radiation in the absorber. By means of the connection of the concentrator cushion to the longitudinal members on the top and bottom sides, the shape of the concentrator cushion can also be maintained reliably in response to large external loads and regardless of the pivoting angle of the concentrator cushion. In this embodiment, in particular the local retaining plates between the pivoting apparatus and the concentrator, which are provided in the prior art, can be renounced. On the one hand, the design distinguishes itself in that wind loads can be transferred efficiently via the longitudinal members. On the other hand, it is advantageous that the pivoting of the concentrator cushion does not have a significant effect on the curvature of the reflector film between the upper and lower hollow spaces of the concentrator cushion due to the retainer on the longitudinal members.
The upper longitudinal member is preferably designed like the lower longitudinal member. The afore-described embodiment variants of the lower longitudinal member and its securing to the lower passage opening may therefore be implemented correspondingly with the upper longitudinal member at the upper passage opening of the concentrator cushion. Accordingly, the longitudinal belts of the upper longitudinal member, on the one hand, may be connected in a substantially air-tight manner with the longitudinal edges of the cover film element which are adjacent to the upper passage opening. On the other hand, the longitudinal belts of the upper longitudinal member may be connected in a substantially air-tight manner with the lateral edge regions of an upper sealing film strip which extends between the longitudinal belts of the upper longitudinal member preferably substantially across the entire width of the upper passage opening.
To make it possible for the concentrator cushion to track the sun's path, i.e. the current position of the sun above the location, it is beneficial if the pivoting apparatus comprises at least one pivoting element, in particular a pivoting ring, which surrounds the concentrator cushion in its circumferential direction, to the inner side of which pivoting element the lower longitudinal member, preferably also the upper longitudinal member, of the retaining apparatus are secured. Preferably, at the inner side of the pivoting element which faces the concentrator cushion, the bottom longitudinal member to which the tensioning element for the reflector foil is secured, is mounted, on the one hand, and the upper longitudinal member on which the absorber for the solar radiation is suspended, is mounted, on the other hand. Such pivoting rings are known per se in the prior art, see, e.g., WO 2012/145774. In contrast to this, the pivoting movement of the pivoting element in the case of the embodiment at hand is transferred to the concentrator cushion via the upper longitudinal member on the top side of the concentrator cushion, on the one hand, and via the lower longitudinal member on the bottom side of the concentrator cushion, on the other hand. The geometry of the reflector film can be reliably ensured in this way, regardless of the pivoting angle of the concentrator cushion. Preferably, no further connections are provided between the pivoting apparatus and the concentrator cushion. According to this, the connections between the upper or lower longitudinal member, respectively, which connections extend in the longitudinal direction, and the concentrator cushion are preferably the only connections between the pivoting apparatus and the retaining apparatus for the concentrator cushion.
To transfer loads, for example wind loads, acting on the concentrator cushion, it is favorable if provision is made for a plurality of pivoting elements, in particular pivoting rings, which are spaced apart in the longitudinal direction of the concentrator cushion and to the inner side of which pivoting elements the upper longitudinal member and the lower longitudinal member of the retaining apparatus are secured. According to this, the longitudinal members are secured to the pivoting elements at defined intervals, wherein the concentrator cushion passes through the individual pivoting elements.
To ensure the geometry of the concentrator cushion and the arrangement of the absorber in the focus area of the reflector film even in the case of high exterior loads, it is favorable if the upper longitudinal member and/or the lower longitudinal member extends at least over more than half of the length of the concentrator cushion, wherein the upper longitudinal member and/or the lower longitudinal member preferably extends between a front end piece and a rear end piece on the front sides of the concentrator cushion. It is thus particularly favorable if the upper longitudinal member and the lower longitudinal member extend substantially over the entire length of the concentrator cushion. In the case of this embodiment, the longitudinal members end adjacent to the end pieces of the concentrator cushion, by means of which the upper and the lower hollow spaces of the concentrator cushion are closed in a substantially air-tight manner. The passage openings of the concentrator cushion extend according to the longitudinal members in longitudinal direction of the concentrator cushion.
To anchor the pivoting apparatus on a bottom structure, provision can be made for an anchoring apparatus which preferably comprises a suspension apparatus for suspending the pivoting apparatus. The pivoting apparatus is set up to pivot the concentrator cushion, preferably about its longitudinal axis. In this embodiment the pivoting apparatus, to which the concentrator cushion is secured in the operating state, is preferably supported substantially completely by the suspension apparatus. For the purposes of this disclosure, the suspension of the pivoting apparatus means that the securing locations between the suspension apparatus and the pivoting apparatus are arranged exclusively above a plane which comprises the center of mass of the pivoting apparatus. The terms “top” and “bottom” here refer to the operating position of the device. This embodiment in particular has the advantage that the external loads, such as wind forces, can be absorbed particularly efficiently and can be transferred to a foundation at the location. It is advantageous in particular that the cushion-shaped or tubular concentrator, respectively, can be kept largely free from external influences. The concave curvature of the reflector film between the upper and the lower hollow spaces of the concentrator can thus be accurately maintained, so that the solar radiation is focused on the absorber with a high efficiency. This design is further advantageous to the effect that the pivoting apparatus can be embodied so as to be slimmer than in the prior art. Material costs can thus be saved. The level of clouding of the reflector film is furthermore reduced, whereby the efficiency can be further increased.
For suspending the pivoting apparatus for the concentrator cushion it is favorable if the suspension apparatus comprises at least one support frame, preferably a plurality of support frames, which are arranged so as to be spaced apart in the longitudinal direction of the concentrator cushion, wherein the at least one support frame in each case comprises at least a first frame element on the one longitudinal side of the concentrator cushion and a second frame element on the other longitudinal side of the concentrator cushion. Advantageously, the support frame can be produced in a simple manner from standard profiles, which already leads to significant cost advantages in the case of small quantities.
To increase the stability of the suspension apparatus, it is advantageous if the support frame comprises a third frame element above the concentrator cushion, which connects the first frame element on the one longitudinal side of the concentrator cushion to the second frame element on the other longitudinal side of the concentrator cushion. In the case of this embodiment, the support frame thus extends from the one longitudinal side of the concentrator cushion beyond the top side of the concentrator cushion to the other longitudinal side of the concentrator cushion, so that the concentrator cushion is arranged completely inside the support frame in the assembled operating state. The pivoting apparatus is preferably suspended on the bottom side of the support frame. According to this, the pivoting apparatus is preferably framed substantially completely by the support frame. This embodiment has turned out to be particularly favorable for absorbing the forces, for example wind forces, which appear during operation.
For the concentrator cushion to track the sun's path, it is advantageous if provision is made between the suspension apparatus and the pivoting apparatus for a pivot bearing apparatus, in particular a roller bearing. Such roller bearings are known per se in the prior art, see, e.g., WO 2012/145774. The roller bearing has roller elements which are in particular provided on a traveling crane. The roller elements are connected to a drive, wherein, in the driven state, the roller elements generate a torque, which effects a pivoting of the pivoting apparatus with the concentrator cushion about an axis, in particular about the longitudinal axis of the concentrator cushion, as a result of a frictional connection in response to the rolling on the pivoting apparatus.
The invention will be explained in more detail below by means of exemplary embodiments, which are illustrated in the drawing, but to which the invention is not to be limited.